Method for coordinating transmissions between different communications apparatuses and communications apparatuses utilizing the same

ABSTRACT

A communications apparatus is provided. A controller module generates a suggested sub-frame pattern describing suggested arrangement of one or more almost blank sub-frame(s) in one or more frame(s) and schedules control signal and/or data transmissions according to the suggested sub-frame pattern. A transceiver module transmits at least a first signal carrying information regarding the suggested sub-frame pattern to a peer communications apparatus. The peer communications apparatus does not schedule data transmissions in the almost blank sub-frame(s).

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/356,090 filed 2010 Jun. 18 and entitled “INTERCELL INTERFERENCECOORDINATION OF DOWNLINK CONTROL CHANNELS IN LTE HETEROGENEOUS NETWORKOF MACRO PLUS HOME ENODEBS DEPLOYMENT”, U.S. Provisional Application No.61/356,092, filed 2010 Jun. 18 and entitled “INTERFERENCE MITIGATION INHETEROPENEOUS NETWORKS”, U.S. Provisional Application No. 61/356,727,filed 2010 Jun. 21 and entitled “INTERCELL INTERFERENCE COORDINATION INA HETEROGENEOUS NETWORK BY SUBFRAMES MUTING AN INTERFERENCE REPORT”,U.S. Provisional Application No. 61/388,681, filed 2010 Oct. 1 andentitled “INTER-CELL INTERFERENCE COORDINATION WITHOUT BAKHAUL SIGNALINGBETWEEN MACRO AND FEMTO ENBS” and U.S. Provisional Application No.61/408,868, filed 2010 Nov. 1 and entitled “DESIGN OF ALMOST BLANKSUBFRAME (ABS) PATTERN IN FDD AND TDD COMMUNICATIONS SYSTEM”. The entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a wireless network communications, and moreparticularly to uplink/downlink transmission coordination betweendifferent cells to avoid inter-cell interference in wirelesscommunications systems.

2. Description of the Related Art

Due to mobile communication technology advancements in recent years,various communications services, such as voice call services, datatransfer services, and video call services, etc., may be provided tousers regardless of their locations. Most mobile communications systemsare multiple access systems in which access and wireless networkresources are allocated to multiple users. The multiple accesstechnologies employed by the mobile communications systems include the1× Code Division Multiple Access 2000 (1×CDMA 2000) technology, the 1×Evolution-Data Optimized (1× EVDO) technology, the Orthogonal FrequencyDivision Multiplexing (OFDM) technology, and the Long Term Evolution(LTE) technology. Evolved from the LTE, the LTE Advanced is a majorenhancement of the LTE standard. The LTE Advanced should be compatiblewith LTE equipment, and should share frequency bands with the LTEcommunications system. One of the important LTE Advanced benefits is itsability to take advantage of advanced topology networks, whereinoptimized heterogeneous networks have a mix of macros with low powernodes such as picocells, femtocells and new relay nodes.

FIG. 1 shows an exemplary heterogeneous network (HetNet) deployment.Within the coverage area 100 of a macro evolved node B (eNB) 101,several low power nodes having smaller coverage areas are deployed so asto improve the overall system capacity. As shown in the figure, a picoeNB (also called a picocell) 102, a femto eNB (also called a femtocell)103 and a relay eNB 104 are deployed with the coverage area 100 of themacro eNB 101. However, such HetNet deployment may cause undesiredinter-cell interference. For example, suppose that the user equipment(UE) 202 camps on the pico eNB 102 as a serving cell. When the UE 202moves to the cell edge of pico eNB 102, the signal transmitted by themacro eNB 101 adjacent to the UE 202 may become a strong interference tothe UE 202 since the power of the signal transmitted by the pico eNB 102may be weak when the signal reaching the UE 202. For another example,when a UE 201 not belong to the closed subscriber group (CSG) of thefemto eNB 103 moves to the coverage area thereof, the signal transmittedby the femto eNB 103 may also become a strong interference to the UE201. For yet another example, the signal transmitted by the macro eNB101 may also be an interference to the UE 203 when the relay eNB 104 istransmitting signal or data to the UE 203 at the same time.

In order to solve the above-mentioned problems, methods and apparatusfor uplink/downlink transmission coordination between different cells toavoid inter-cell interference in wireless Orthogonal Frequency DivisionMultiple Access (OFDMA) communications systems are provided.

BRIEF SUMMARY OF THE INVENTION

Communications apparatuses and methods for coordinating transmissionsbetween different communications apparatuses are provided. An embodimentof a communications apparatus comprises a controller module and a radiofrequency (RF) module. The controller module generates a suggestedsub-frame pattern describing suggested arrangement of one or more almostblank sub-frame(s) in one or more frame(s) and schedules control signaland/or data transmissions according to the suggested sub-frame pattern.The radio frequency module transmits at least a first signal carryinginformation regarding the suggested sub-frame pattern to a peercommunications apparatus. The peer communications apparatus does notschedule data transmissions in the almost blank sub-frame(s).

Another embodiment of a communications apparatus comprises a controllermodule and a radio frequency (RF) module. The controller modulegenerates a predetermined sub-frame pattern describing arrangement ofone or more almost blank sub-frame(s) in one or more frame(s) andschedules control signal and/or data transmissions according to thepredetermined sub-frame pattern. The controller module does not scheduledata transmission in the almost blank sub-frame(s). The RF moduletransmits at least a first signal carrying information regarding thepredetermined sub-frame pattern to a peer communications apparatus.

An embodiment of a method for coordinating transmissions betweendifferent communications apparatus comprises: generating a predeterminedsub-frame pattern describing arrangement of one or more almost blanksub-frame(s) in one or more frame(s); informing at least a peercommunications apparatus about the predetermined sub-frame pattern; andscheduling control signal and/or data transmissions according to thepredetermined sub-frame pattern.

Another embodiment of a communications apparatus comprises a controllermodule and a radio frequency (RF) module. The controller module obtainsinformation regarding a Hybrid Automatic Repeat Request (HARQ) roundtrip time (RTT) in an HARQ process, arranges one or more almost blanksub-frame(s) in one or more frame(s) according to the HARQ RTTinformation and generates a sub-frame pattern describing the arrangementof the almost blank sub-frame(s). The HARQ RTT is defined by thecommunications system. The RF module transmits at least a signalcarrying information regarding the sub-frame pattern to a peercommunications apparatus in the communications system.

Another embodiment of a method for coordinating transmissions betweendifferent communications apparatus comprises: obtaining informationregarding a Hybrid Automatic Repeat Request (HARQ) round trip time (RTT)in an HARQ process defined by the communications system; and arrangingone or more almost blank sub-frame(s) in one or more frame(s) accordingto the HARQ RTT.

Another embodiment of a method for coordinating transmissions betweendifferent communications apparatus comprises: obtaining a sub-frameindicator carried in a first control signal transmitted in a controlregion of a first sub-frame received from an evolved node B (eNB),wherein the sub-frame indicator indicates resource allocation of one ormore sub-frame following the first sub-frame; determining whether asecond sub-frame following the first sub-frame and received from the eNBis an almost blank sub-frame according to the sub-frame indicator; andwhen the second sub-frame is not the almost blank sub-frame, obtaininginformation regarding a start position of a data region of the secondsub-frame from a second control signal transmitted in a control regionof the second sub-frame.

Another embodiment of a method for coordinating transmissions betweendifferent communications apparatus comprises carrying a sub-frameindicator in a first control signal to be transmitted in a controlregion of a first sub-frame to indicate a user equipment whether asecond sub-frame following the first sub-frame is an almost blanksub-frame.

Another embodiment of a method for a communications system to assign anAlmost Blank Sub-frame (ABS) pattern comprises: collecting one or moreneighbor eNB(s)'s information; identifying at least one victim eNB whichserves one or more UE(s) interfered by the communications system basedon the collected neighbor eNB(s)'s information; and assigning the ABSpattern to the victim eNB such that an interference within a cell of thevictim eNB is reduced.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 shows an exemplary heterogeneous network (HetNet) deployment;

FIG. 2 a is a block diagram illustrating a communications apparatusaccording to an embodiment of the invention;

FIG. 2 b a is a block diagram illustrating a communications apparatusaccording to an embodiment of the invention;

FIG. 3 shows downlink radio resource allocations utilized according toan embodiment of the invention;

FIG. 4 shows a downlink sub-frame arrangement between an aggressor eNBand a victim eNB to avoid inter-cell interference according to a conceptof the invention;

FIG. 5 is a flow chart showing a method for coordinating transmissionsbetween different communications apparatuses according to a first aspectof the invention;

FIG. 6 is a message flow showing the HARQ process according to anembodiment of the invention;

FIG. 7 shows an exemplary arrangement of several ABSs scheduled by anaggressor eNB and the corresponding HARQ messages scheduled by a victimeNB according to an embodiment of the invention;

FIG. 8 is a table showing the TDD uplink/downlink (UL/DL) configurationsin the communications system according to an embodiment of theinvention;

FIG. 9 a shows the values of HARQ parameter k1 in TDD UL/DLconfigurations 1-6 according to an embodiment of the invention;

FIG. 9 b shows the values of HARQ parameter k2 in TDD UL/DLconfigurations 1-6 according to an embodiment of the invention;

FIG. 10 shows an exemplary arrangement of several ABSs scheduled by anaggressor eNB and the corresponding HARQ messages scheduled by a victimeNB according to another embodiment of the invention; and

FIG. 11 shows an exemplary arrangement of several ABSs scheduled by anaggressor eNB according to yet another embodiment of the invention;

FIG. 12 a shows a first arrangement of values of HARQ parameter k1 inTDD UL/DL configuration 0 according to an embodiment of the invention;

FIG. 12 b shows a second arrangement of values of HARQ parameter k1 inTDD UL/DL configuration 0 according to another embodiment of theinvention;

FIG. 13 a shows a first arrangement of values of HARQ parameter k2 inTDD UL/DL configuration 0 according to an embodiment of the invention;

FIG. 13 b shows a second arrangement of values of HARQ parameter k2 inTDD UL/DL configuration 0 according to another embodiment of theinvention;

FIG. 14 is a flow chart showing a method for coordinating transmissionsbetween different communications apparatuses according to a secondaspect of the invention;

FIG. 15 shows a downlink sub-frame arrangement to describe the conceptof cross sub-frame arrange for ABS according to a third aspect of theinvention;

FIG. 16 is a flow chart showing a method for cross sub-frame schedulingfor ABS according to a first embodiment of a third aspect of theinvention;

FIG. 17 is a flow chart showing a method for cross sub-frame schedulingfor ABS according to a second embodiment of a third aspect of theinvention;

FIG. 18 is a flow chart showing a method for cross sub-frame schedulingfor ABS according to a third embodiment of a third aspect of theinvention;

FIG. 19 is a flow chart showing a method for a communications system toassign an ABS pattern according to an embodiment of the invention; and

Table 1 shows the indices of sub-frames that may be set as ABSs fordifferent TDD UL/DL configurations.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

FIG. 2 a is a block diagram illustrating a communications apparatusaccording to an embodiment of the invention. The communicationsapparatus 200 may be an User Equipment (UE) in the service network asshown in FIG. 1. The operations of the service network may be incompliance with a communication protocol. In one embodiment, the servicenetwork may be a Long Term Evolution (LTE) system or an LTE Advancedsystem. The communications apparatus 200 may comprise at least abaseband module 210, a Radio Frequency (RF) module 220 and a controllermodule 230. The baseband module 210 may comprise multiple hardwaredevices to perform baseband signal processing, including Analog toDigital Conversion (ADC)/Digital to Analog Conversion (DAC), gainadjusting, modulation/demodulation, encoding/decoding, and so on. The RFmodule 220 may receive RF wireless signals, convert the received RFwireless signals to baseband signals, which are processed by thebaseband module 210, or receive baseband signals from the basebandmodule 210 and convert the received baseband signals to RF wirelesssignals, which are later transmitted. The RF module 220 may alsocomprise multiple hardware devices to perform radio frequencyconversion. For example, the RF module 220 may comprise a mixer tomultiply the baseband signals with a carrier oscillated in the radiofrequency of the wireless communications system, wherein the radiofrequency may be 900 MHz, 1900 MHz, or 2100 MHz utilized in UniversalMobile Telecommunications System (UMTS) systems, or may be 900 MHz, 2100MHz, or 2.6 GHz utilized in the LTE systems, or others depending on theradio access technology (RAT) in use. The controller module 230 controlsthe operation of the baseband module 210 and RF module 220 and otherfunctional components, such as a display unit and/or keypad serving asthe MMI (man-machine interface), a storage unit storing data and programcodes of applications or communication protocols, or others. In additionto the UMTS system and the LTE system, it is to be understood that theinvention may be applied to any future RATs.

FIG. 2 b is a block diagram illustrating a communications apparatusaccording to another embodiment of the invention. The communicationsapparatus 250 may be an evolved node B (eNB) in the service network asshown in FIG. 1. The communications apparatus 250 may comprise at leasta baseband module 260, a transceiver module 270 and a controller module280. The transceiver module 270 may transmit and receive signals viawireless or wired manner. Noted that according to the embodiment of theinvention, the eNB may transmit control or/and data signal(s) to one ormore UEs and communicate with other eNBs via wireless or wiredconnection. For example, the transceiver module 270 may comprise a RFmodule or directly act as RF module, and the operations of the RF moduleare similar to the RF module 220 in FIG. 2 a. In some embodiments, thetransceiver module may communicate with other eNBs via backhaulconnection. The operations of the baseband module 260 and the controllermodule 280 are similar to that of the baseband module 210 and thecontroller module 230 as shown in FIG. 2 a. Therefore, the detaileddescriptions of the baseband module 260 and the controller module 280may refer to that of the baseband module 210 and the controller module230 as described above, and are omitted here for brevity. Note thataccording to the embodiment of the invention, because the eNB isresponsible for serving one or more UEs in the serving network, thecontroller module 280 may further schedule control signal and datatransmissions for transmitting control signals and data to the UE(s) inthe serving network. For example, the controller module 280 may comprisea scheduler module 290, which is arranged to schedule the control signaland data transmissions. Note that in some embodiments, the transmissionscheduling may be directly performed by the controller module 280.Therefore, a dedicated scheduler module 290 may an optional choice basedon different design requirements, and the invention should not belimited what is shown in FIG. 2 b. Note also that the controller module230/280 may also be integrated into the baseband module 210/260,depending on different design requirements, and the invention should notbe limited what is shown in FIG. 2 a and FIG. 2 b.

FIG. 3 shows downlink radio resource allocations according to anembodiment of the invention. Here, downlink means the signals aretransmitted from an eNB to an UE. As shown in FIG. 3, a downlinksub-frame 300 is composed of a control region 301 and a data region 302.In the data region 302, data signals of different UEs are transmitted indifferent sub-bands (i.e. by using different sub-carriers), where eachbar in the figure represents a frequency sub-band. However, in thecontrol region, control signals of different UEs are transmitted overthe full downlink band. When downlink control signals are simultaneouslytransmitted by adjacent eNBs in the heterogeneous network as shown inFIG. 1, the important downlink control signals transmitted by one eNBmay suffer the interference from another eNB and therefore, inter-cellinterference happens. To solve the problems, several methods foruplink/downlink transmission coordination between different cells toavoid inter-cell interference in wireless communications systems and thecommunications apparatus thereof are provided.

Referring back to FIG. 1, as previously described, the signaltransmitted by the macro eNB 101 adjacent to the UE 202 may become astrong interference to the UE 202 when the UE 202 moves to the cell edgeof pico eNB 102. In this case, the macro eNB 101 may be regarded as anaggressor eNB, the UE 202 may be regarded as a victim UE and the picoeNB 102 may be regarded as a victim eNB since the downlink signaltransmitted by the pico eNB 102 may be interfered by the downlink signaltransmitted by the macro eNB 101. Similarly, for the case when downlinksignal transmitted by the femto eNB 103 to interfere with the downlinksignal transmitted by the macro eNB 101, the femto eNB 103 may beregarded as an aggressor eNB, the UE 201 may be regarded as a victim UEand the macro eNB 101 may be regarded as a victim eNB. Further, for thecase when downlink signal transmitted by the macro eNB 101 to interferewith the downlink signal transmitted by the relay eNB 104, the macro eNB101 may be regarded as an aggressor eNB, the UE 203 may be regarded as avictim UE and the relay eNB 104 may be regarded as a victim eNB.

FIG. 4 shows a downlink sub-frame arrangement between an aggressor eNBand a victim eNB to avoid inter-cell interference according to a conceptof the invention. In the embodiment, the aggressor eNB may blank one ormore sub-frame(s) in one or more frame(s) for victim eNBs so that thevictim eNBs may schedule the control signal and/or data transmissions totransmit the control signal and/or data to the victim UE in thecorresponding sub-frames. Generally, one frame may comprise 10sub-frames, and one sub-frame has duration of 1 ms and comprises 14 OFDMsymbols. The victim UEs are those suffer interference from the aggressoreNB. The sub-frame blanked by the aggressor eNB is called an almostblank sub-frame (ABS). In the ABS, the aggressor eNB may not scheduledata transmission, and only schedule fewer control signal transmissionsthan in a normal sub-frame. Because data transmission is not scheduledin the ABS, the control signals to be transmitted in the ABS can befewer than that have to be transmitted in a normal sub-frame. Forexample, in the ABS, the Physical Control Format Indicator Channel(PCFICH) control signals and Physical Downlink Control Channel (PDCCH)control signals and are not transmitted, where the PCFICH control signalis utilized to specify how many OFDM symbols are used to transmit thecontrol channels so the receiver UE knows where to find controlinformation, and the PDCCH control signal is utilized to specifyresource allocation and modulation and coding scheme of the data signals(to be transmitted in the data region). The control signals that arestill transmitted in the control region of an ABS may comprise, forexample and not limited to, the common control signals (such as a commonreference signal (CRS), synchronization signal, system information . . .etc.) and paging signal.

As shown in FIG. 4, the (p+1)-th sub-frame is arranged by the aggressoreNB as an ABS. Therefore, the victim eNB may schedule the control signaland/or data transmissions of the victim UE in the (p+1)-th sub-frame.The victim eNB may obtain information regarding which UE(s) connectedthereto is/are the victim UE according to, for example and not limitedto, the measurement report provided by the UE(s). To be more specific,if the measurement report shows that the power of signals received froma non-serving eNB have exceed a predetermined threshold, the UE may beregarded as a victim UE. In the following paragraphs, three aspects ofthe invention will be introduced. According to a first aspect of theinvention, methods for coordinating the sub-frame pattern whichdescribes the arrangement of one or more ABS(s) and the communicationsapparatuses utilizing the same are provided.

According to an embodiment of the invention, the controller module (suchas the controller module 280) of an aggressor eNB may first generate apredetermined sub-frame pattern, which describes predeterminedarrangement of one or more ABS(s) in one or more frame(s), and inform atleast a victim eNB about the predetermined sub-frame pattern bytransmitting at least a first signal carrying information regarding thepredetermined sub-frame pattern to the victim eNB via the transceivermodule (such as the transceiver module 270). Note that in this case, theinformed victim eNB may be regarded as a peer communications apparatuswith respect to the aggressor eNB. The controller module (or thescheduler module 290) of the aggressor eNB may further schedule controlsignal and/or data transmissions according to the predeterminedsub-frame pattern. As previously described, the aggressor eNB may notschedule data transmission in the ABS(s), and may schedule fewer controlsignal transmissions in the ABS(s) than in normal sub-frames aspreviously described.

For the victim eNB, after receiving the first signal from the aggressoreNB, the controller module (such as the controller module 280) of thevictim eNB may further generate a suggested sub-frame pattern describingsuggested arrangement of one or more ABS(s) based on the predeterminedsub-frame pattern, and report the suggested sub-frame pattern to theaggressor eNB via the transceiver module (such as the transceiver module270). Note that in this case, the aggressor eNB may be regarded as apeer communications apparatus with respect to the victim eNB. Thecontroller module of the victim eNB may transmit a second signalcarrying information regarding the suggested sub-frame pattern to theaggressor eNB via the transceiver module. According to an embodiment ofthe invention, the suggested sub-frame pattern is a subset of thepredetermined sub-frame pattern, and the controller module (or thescheduler module 290) of the victim eNB may schedule control signaland/or data transmissions according to the suggested sub-frame pattern.The predetermined sub-frame pattern and suggested sub-frame pattern maybe represented as a bit-string which comprises a plurality of bits,where each bit is utilized to describe whether a corresponding sub-frameis an almost blank sub-frame (ABS) or a normal sub-frame. For example,the predetermined sub-frame pattern may be {11000000}, where the ‘1’indicates that the corresponding sub-frame is an ABS, and the ‘0’indicates that the corresponding sub-frame is a normal sub-frame. Thesuggested sub-frame pattern determined by the victim eNB may be{10000000}, which is an subset of the predetermined sub-frame pattern.

According to another embodiment of the invention, the victim eNB mayalso carry information regarding a number of suggested (or useful)ABS(s), or a ratio of the number of suggested (or useful) ABS(s) to anumber of total ABS(s) arranged in the predetermined sub-frame patternin the second signal. Note that in yet some embodiments of theinvention, the victim eNB may also directly generate the suggestedsub-frame pattern according to information collected from the served UEs(for example, which UE(s) in the service network is/are the victims andwhich sub-frame(s) is/are utilized to transmit important control signalsto the victim UE(s)) without receiving the predetermined sub-framepattern in advance, and provide the suggested sub-frame pattern to theaggressor eNB. In this manner, in the suggested ABS(s), the aggressoreNB is suggested to schedule only a fewer of necessary control signaltransmissions, and no data transmissions.

Note that in the invention, the sub-frame pattern may be semi-staticallyupdated. As previously described, the victim eNB may report a number ofsuggested (or useful) ABS(s), a ratio of the number of suggested (oruseful) ABS(s) to a number of total ABS(s) arranged in the predeterminedsub-frame pattern, and/or the suggested sub-frame pattern to theaggressor eNB (hereinafter called the reported information) when thepredetermined sub-frame pattern is not appropriate for the victim eNB.For example, when the ratio of the number of suggested (or useful)ABS(s) to a number of total ABS(s) arranged in the predeterminedsub-frame pattern reported by the victim eNB approaches 1, it means thatthe number of total ABS(s) arranged in the predetermined sub-framepattern may be not enough for the victim eNB to arrange the controlsignal and/or data transmissions for the victim UEs. The aggressor eNBmay collect the reported information from its neighboring eNBs whereneighboring eNBs is the eNB in the aggressor eNB's cell coverage or theeNB of its neighboring cell, and update the predetermined sub-framepattern based on the collected reported information to obtain an updatedsub-frame pattern.

The aggressor eNB may further transmit at least a third signal carryinginformation regarding the updated sub-frame pattern to its neighboringeNB(s). Note that in this case, the victim eNB may be regarded as a peercommunications apparatus with respect to the aggressor eNB. Both theaggressor eNB and the victim eNB(s) may schedule the control signaland/or data transmissions according to the updated sub-frame pattern.According to an embodiment, the predetermined, suggest and updatedsub-frame patterns may be transmitted in compliance with X2 protocol.The X2 protocol is defined by the communications system for establishingcommunications between different eNBs. According to another embodiment,the predetermined, suggest and updated sub-frame patterns may betransmitted via the air interface in compliance with the protocoldefined by the RAT in use. The air interface is the wirelesstransmission path established the UE and the eNB or between the relayeNB and macro eNB.

FIG. 5 is a flow chart showing a method for coordinating transmissionsbetween different communications apparatuses according to the firstaspect of the invention. The eNB (either an aggressor or a victim eNB)may first generate a sub-frame pattern describing arrangement of one ormore almost blank sub-frame(s) in one or more frame(s) (Step S502), andthe sub-frame pattern may be the above-mentioned predetermined,suggested or updated sub-frame pattern generated by the aggressor orvictim eNB. Next, the eNB may inform at least a peer communicationsapparatus (for example, a peer aggressor or victim eNB, depending onwhether the sub-frame pattern is generated by the victim eNB or theaggressor eNB) about the sub-frame pattern (Step S504). As previouslydescribed, the eNB may inform the peer communications apparatus bytransmitting a signal carrying information regarding the sub-framepattern. Note that in some embodiments of the invention, the eNB (eitherthe aggressor or the victim eNB) may also carry information regarding aframe and/or sub-frame index offset to indicate from which frame and/orsub-frame should the sub-frame pattern begin to be applied. Finally, theeNB may schedule control signal and/or data transmissions according tothe sub-frame pattern (Step S506). For example, in some embodiments ofthe invention, the eNB may schedule fewer control signal transmissionsand no data transmissions in the ABS(s).

According to a second aspect of the invention, methods for determiningsub-frame index (indices) of one or more ABS(s) and the communicationsapparatuses utilizing the same are provided. According to an embodimentof the invention, because synchronous Hybrid Automatic Repeat Request(HARQ) transmission scheme is adopted in the communications system forerror correction, the sub-frame index (indices) of the ABS(s) ispreferably determined with consideration of the completeness of an HARQprocess. Typically, the communications apparatus can transmit/retransmitthe HARQ messages in a periodic manner where consecutive HARQ messagesare spaced by about a round trip time (RTT) delay. The HARQ messages maycomprise an uplink grant message and an acknowledgement (ACK)/negativeacknowledgement message (NACK) (which will be discussed in more detailedin the following paragraphs). An HARQ process may begin when the uplinkgrant message is transmitted, and end when an ACK/NACK message istransmitted. The time span between the transmissions of the uplink grantmessage and the ACK/NACK message defines the HARQ round trip time.

FIG. 6 is a message flow showing the HARQ process according to anembodiment of the invention. Suppose that a sub-frame offset between anuplink grant message transmission and uplink data transmission isdefined by communications system as the k1, and a sub-frame offsetbetween the uplink data transmission and an acknowledgment (ACK) or anegative acknowledgment (NACK) message transmission is defined bycommunications system as the k2, the HARQ RTT is (k1+k2). Therefore, asshown in FIG. 6, the eNB may transmit the uplink grant message (theUL_Grant as shown) to the UE in the n-th sub-frame, wherein n is anon-negative integer. After receiving the UL grant message, the UE maytransmit the uplink data (the UL_Data as shown) to the eNB in the (n+k1)th sub-frame. The eNB may further transmit the ACK/NACK message (theACK/NACK as shown) in the (n+k1+k2) th sub-frame for informing the UEabout whether uplink data have been received or not. When the uplinkdata is not received (i.e. an NACK message is transmitted by the eNB),or when there is still some uplink data have to be transmitted, the UEmay further retransmit or transmit the uplink data to the eNB in the(n+2k1+k2) th sub-frame. The eNB may further transmit the ACK/NACKmessage in the (n+2k1+2k2) th sub-frame for informing the UE aboutwhether uplink data have been received or not.

According to an embodiment of the invention, because the uplink grantmessage and the ACK/NACK message are important control signals to betransmitted in the control region (such as the control region 301 asshown in FIG. 3), the controller module (such as the controller module280) of an eNB (either an aggressor or a victim eNB) may arrange one ormore ABS(s) in one or more frame(s) according to the HARQ RTT in an HARQprocess and, as previously described, generate a sub-frame patterndescribing the arrangement of the ABS(s). For example, the ABS(s) in thesub-frame pattern may be arranged according to a transmission period ofthe uplink grant message and the ACK/NACK message.

To be more specific, when the HARQ RTT is defined by (k1+k2) sub-frames,the controller module (such as the controller module 280) may arrangethe almost blank sub-frame(s) in the following rule:

Given n and m are non-negative integers, when n-th is almost blanksub-frame, [n+m*(k1+k2)]-th sub-frame(s) are almost blank sub-frame.

Note that based on the concept of the invention, at least one ABS in thesub-frame pattern is arranged in a sub-frame utilized by a victim eNB totransmit an uplink grant message for granting a victim UE who want totransmit uplink data thereto, and/or at least one ABS in the sub-framepattern is arranged in a sub-frame utilized by the victim eNB totransmit an ACK/NACK message for informing the victim UE about whetherthe uplink data transmitted by the victim UE in response to the receiveduplink grant message have been received by victim eNB. Therefore, thevictim eNB and the victim UE can successfully complete an HARQ processwithout being interfered by the aggressor eNB.

For example, suppose that in a frequency division duplex (FDD) mode(that is, the uplink and downlink data are transmitted in differentfrequency bands in an FDD manner), it is defined by the LTE system thatk1=4 and k2=4. Therefore, in a preferred embodiment, the aggressor eNBmay blank the (n+m*8)-th sub-frame(s) to avoid inter-cell interferencewhen n-th subframe is assigned as an almost blank sub-frame.

FIG. 7 shows an exemplary arrangement of several ABSs scheduled by anaggressor eNB and the corresponding HARQ messages scheduled by a victimeNB according to an embodiment of the invention. As shown in FIG. 7, theaggressor eNB blanks the first and the 9-th sub-frame in the x-th frameand the 7-th sub-frames in the (x+1)-th frame as the almost blanksub-frames. Therefore, the sub-frame index offset between the ABSs wouldbe a multiple of 8 (that is, a multiple of (k1+k2)). The victim eNB maytransmit an uplink grant message UL_Grant in the first sub-frame in thex-th frame, and receive the uplink data UL_Data from the UE in the 5-thsub-frame in the x-th frame. The victim eNB may further transmit anacknowledge message ACK/NACK in the 9-th sub-frame in the x-th frame,receive the uplink data UL_Data from the UE in the third sub-frame inthe (x+1)-th frame, and transmit an acknowledge message ACK/NACK in the7-th sub-frames in the (x+1)-th frame. Because the uplink grant messageUL_Grant and the acknowledge message ACK/NACK are transmitted during theABS interval arranged by the aggressor eNB, the uplink grant message andthe acknowledge message can be transmitted without being interfered.

According to another embodiment of the invention, the controller modulemay also arrange the almost blank sub-frame(s) in the [n+m*(k1+k2)]-thsub-frame(s) when the n-th sub-frame is assigned as an almost blanksub-frame while operating in a time division duplex (TDD) mode (that is,the uplink and downlink data are transmitted in a TDD manner in the samefrequency band). FIG. 8 is a table showing the TDD uplink/downlink(UL/DL) configurations in the communications system according to anembodiment of the invention. As shown in the table, the letter ‘D’represents that the corresponding sub-frame is a downlink sub-frame, theletter ‘U’ represents that the corresponding sub-frame is a uplinksub-frame, and the letter ‘S’ represents that the correspondingsub-frame is a special sub-frame. Note that the fore-portion of thespecial sub-frame is utilized for downlink transmission, thelater-portion of the special sub-frame is utilized for uplinktransmission, and a silence region is arranged in the middle of thespecial sub-frame between the downlink and uplink transmissions. Asshown in FIG. 8, there are seven kinds of configurations defined by thecommunications system, each having different ratios of uplink sub-framenumber to downlink frame number.

For different UL/DL configurations, the HARQ parameters k1 and k2 aredifferent. FIG. 9 a shows the values of HARQ parameter k1 in TDD UL/DLconfigurations 1-6 according to an embodiment of the invention, and FIG.9 b shows the values of HARQ parameter k2 in TDD UL/DL configurations1-6 according to an embodiment of the invention. Note that the numbersshown in the table in FIG. 9 a are values of the corresponding parameterk1 set for different sub-frame index, and the numbers shown in the tablein FIG. 9 b are values of the corresponding parameter k2 set fordifferent sub-frame index.

Take the TDD UL/DL configuration 1 shown in the table in FIG. 9 a as anexample, when an uplink grant message is transmitted by the eNB in thefirst sub-frame, the HARQ parameter k1=6, which means that the UEreceiving the uplink grant message in the first sub-frame can uplinkdata after six sub-frames (that is, the uplink data will be transmittedin the 7-th sub-frame because 1+6=7). Referring now to FIG. 9 b, whenthe uplink data is transmitted in the 7-th sub-frame, the HARQ parameterk2=4, which means that the eNB, that is supposed to receive the uplinkdata in the 7-th sub-frame, is responsible for transmitting the ACK/NCAKmessage after four sub-frames (that is, the ACK/NCAK message will betransmitted in the first sub-frame of a next frame because [(7+4) mod10]=1).

Similarly, take the TDD UL/DL configuration 4 shown in the table in FIG.9 a as an example, when an uplink grant message is transmitted by theeNB in the eighth sub-frame, the HARQ parameter k1=4, which means thatthe UE receiving the uplink grant message in the eighth sub-frame canuplink data after four sub-frames (that is, the uplink data will betransmitted in the second sub-frame of a next frame because [(8+4) mod10]=2). Referring now to FIG. 9 b, when the uplink data is transmittedin the second sub-frame, the HARQ parameter k2=6, which means that theeNB that is supposed to receive the uplink data in the second sub-frameis responsible for transmitting the ACK/NCAK message after sixsub-frames (that is, the ACK/NCAK message will be transmitted in theeighth sub-frame because 2+6=8).

Therefore, in TDD mode, the controller module may also arrange thealmost blank sub-frame(s) in the [n+m*(k1+k2)]-th sub-frame(s) when n-thsub-frame is assigned as an almost blank sub-frame according to thetables as shown in FIG. 9 a and FIG. 9 b. Note that for the TDD UL/DLconfigurations 1-5, it always takes one frame to complete an HARQprocess (that is, (k1+k2)=10 sub-frames=1 frame). In other words, forthe TDD UL/DL configurations 1-5, the offset between the UL grantmessage transmission and the ACK/NACK message transmission is one frame.Therefore, the controller module may arrange the ABS(s) in a fixedlocation in each frame so that a sub-frame index of the arranged ABS(s)can fixed in different frames.

FIG. 10 shows an exemplary arrangement of several ABSs scheduled by anaggressor eNB and the corresponding HARQ messages scheduled by a victimeNB according to another embodiment of the invention. In the embodiment,TDD UL/DL configuration 1 is taken as an example, and the ABSs arearranged by the aggressor eNB in the fourth sub-frame in each frame.Therefore, the victim eNB may transmit an uplink grant message UL_Grantin the fourth sub-frame in the x-th frame and transmit an acknowledgemessage ACK/NACK in the fourth sub-frame in the (x+1)-th frame to avoidbeing interfered by the aggressor eNB.

Referring back to FIG. 9 a and FIG. 9 b, it is noted that for TDD UL/DLconfiguration 6, the HART RTT is not as regular as that for TDD UL/DLconfigurations 1-5. In addition, for TDD UL/DL configuration 0 (whichwill be discussed in the following paragraphs), the HART RTT is alsoirregular. Because the HART RTT is irregular for the TDD UL/DLconfigurations 0 and 6, according to the preferred embodiments of theinvention, the ABS(s) in the sub-frame pattern is/are preferablyarranged in a series of contiguous frames. FIG. 11 shows an exemplaryarrangement of several ABSs scheduled by an aggressor eNB according toyet another embodiment of the invention. In the embodiment, TDD UL/DLconfiguration 6 is taken as an example, and the ABSs are arranged by theaggressor eNB in the 0-th sub-frame of frame 0, first sub-frame of frame1, fifth sub-frame of frame 2, sixth sub-frame of frame 3, ninthsub-frame of frame 4 and 0-th sub-frame of frame 6. Therefore, thevictim eNB may transmit the uplink grant message UL_Grant and theACK/NACK in the ABSs to avoid being interfered by the aggressor eNB.

For TDD UL/DL configuration 0, since the number of uplink sub-frames aremore than the number of the downlink sub-frames, there are twoindicators utilized to indicate which uplink sub-frame is associate withan uplink message or an ACK/NACK message. The first indicator is an ULindex UL_(index), which is a two bits indicator to indicate which uplinksub-frame is associated with a current uplink message. The secondindicator is I_(PHICH), which is used to indicate which sub-frame isassociated with a current Physical Hybrid Automatic Repeat RequestIndicator Channel (PHICH). The ACK/NACK message is transmitted throughthe PHICH.

FIG. 12 a shows a first arrangement of values of HARQ parameter k1 inTDD UL/DL configuration 0 according to an embodiment of the invention,and FIG. 12 b shows a second arrangement of values of HARQ parameter k1in TDD UL/DL configuration 0 according to another embodiment of theinvention. FIG. 13 a shows a first arrangement of values of HARQparameter k2 in TDD UL/DL configuration 0 according to an embodiment ofthe invention, and FIG. 13 b shows a second arrangement of values ofHARQ parameter k2 in TDD UL/DL configuration 0 according to anotherembodiment of the invention. When one of the following two conditions:

-   -   the most significant bit (MSB) of the first indicator UL_(index)        is ‘1’;    -   the ACK/NACK message is received in sub-frame 0 or 5 and        I_(PHICH)=‘0’; is met, the values of HARQ parameter k1 for TDD        UL/DL configuration 0 are set as the table shown in FIG. 12 a.        When one of the following three conditions:    -   the least significant bit (LSB) of the first indicator        UL_(index) is ‘1’;    -   the ACK/NACK message is received in sub-frame 0 or 5 and        I_(PHICH)=‘1’;    -   the ACK/NACK message is received in sub-frame 1 or 6        is met, the values of HARQ parameter k1 for TDD UL/DL        configuration 0 are set as the table shown in FIG. 12 b. In        addition, when I_(PHICH)=‘0’, the values of HARQ parameter k2        for TDD UL/DL configuration 0 are set as the table shown in FIG.        13 a, and when I_(PHICH)‘1’, the values of HARQ parameter k2 for        TDD UL/DL configuration 0 are set as the table shown in FIG. 13        b.

In conclusion, the indices of sub-frames that are preferably set as theABSs for different TDD UL/DL configurations are listed in Table 1.

TABLE 1 the indices of sub-frames that may be set as ABSs for differentTDD UL/DL configurations TDD UL/DL configuration Possible sub-frameindices for ABSs 0 [F, 0], [F + 1, 0], [F + 2, 1], [F + 3, 5], [F + 4,5], [F + 5, 6], [F + 6, NAN] 1 1, 4, 6, 9 2 3, 8 3 0, 8, 9 4 8, 9 5 8 6[F, 0], [F + 1, 1], [F + 2, 5], [F + 3, 6], [F + 4, 9], [F + 5, NAN]

According to an embodiment of the invention, the ABS(s) may be selectedfrom the sub-frames listed in Table 1. Note that for the TDD UL/DLconfigurations 0 and 6, the set of ABS(s) is assumed to be assigned fromframe F, the [i,j] represents the j-th sub-frame of the i-th frame, andthe term ‘NAN’ means there is no ABS arranged in the correspondingframe. Note also that in order to ensure each ACK/NACK message can bedecoded by the victim UE, for the TDD UL/DL configuration 0, when theMSB of the first indicator UL-_(index) is ‘1’, the transmission ofuplink grant message is preferably to be scheduled in frames F and F+3,and when LSB of the first indicator UL_(index) is ‘1’, the transmissionof uplink grant message is preferably to be scheduled in frames F+1 andF+4.

According to an embodiment of the invention, a sub-frame pattern periodfor FDD and TDD modes may also be different. The sub-frame patternperiod is a time period that a sub-frame pattern for describing the ABSarrangement can be applied. For the FDD, because the ABS(s) ispreferably to be arranged in the (n+m*8)-th sub-frame(s), the sub-framepattern may be a bit-string comprising 40 bits to describe the ABSarrangement in 4 contiguous frames and the sub-frame pattern period maybe determined as 40 ms, which is a Least Common Multiple (LCM) of 8 and10, where 8 is a sum of HARQ parameters k1 and k2 for FDD mode and 10 isa length of a frame. For the TDD UL/DL configurations 1-5, because a sumof HARQ parameters k1 and k2 is 10 sub-frames and the system informationblock 1 (SIB 1) is transmitted every two frames, the sub-frame patternmay be a bit-string comprising 20 bits to describe the ABS arrangementin 2 contiguous frames and the sub-frame pattern period may bedetermined as 20 ms. For the TDD UL/DL configuration 0, because the ABSsare preferably arranged in 7 contiguous frames (as shown in Table 1),the sub-frame pattern may be a bit-string comprising 70 bits to describethe ABS arrangement in 7 contiguous frames and the sub-frame patternperiod may be determined as 70 ms. For the TDD UL/DL configuration 6,because the ABSs are preferably arranged in 6 contiguous frames (asshown in Table 1 and FIG. 11), the sub-frame pattern may be a bit-stringcomprising 60 bits to describe the ABS arrangement in 6 contiguousframes and the sub-frame pattern period may be determined as 60 ms.

FIG. 14 is a flow chart showing a method for coordinating transmissionsbetween different communications apparatuses according to the secondaspect of the invention. The eNB (ex, an aggressor eNB) may first obtaininformation regarding HARQ RTT in an HARQ process defined by thecommunications system (Step S1402), and then arrange one or more almostblank sub-frame(s) in one or more frame(s) according to the HARQ RTT(Step S1404). Note that based on the similar concept, the eNB (ex, avictim eNB) may also schedule important control signal (such as theuplink grant message and ACK/NACK message) transmissions for victimUE(s) according to the HARQ RTT (such as the examples shown in FIG. 7,FIG. 10 and FIG. 11).

According to a third aspect of the invention, methods for crosssub-frame scheduling for ABS and the communications apparatusesutilizing the same are provided. FIG. 15 shows a downlink sub-framearrangement to describe the concept of cross sub-frame arrangement forABS according to the third aspect of the invention. Because the ABS isarranged for the purpose to avoid the control signal transmissions of anaggressor eNB to interfere with that of a victim eNB, according to thethird aspect of the invention, the data region of the ABS may still beutilized for data transmission to increase the downlink throughput. Asshown in FIG. 15, the sub-frame p is a normal sub-frame and thesub-frame (p+1) is an ABS with data transmitted therein. However,because the PCFICH and PDCCH control signals are not transmitted in thecontrol region of the sub-frame (p+1), information regarding a startposition of the data region, the resource allocation and modulation andcoding scheme of the data signals of the sub-frame (p+1) cannot beobtained from the control region of the sub-frame (p+1). In this manner,when the data region of the ABS is utilized by the aggressor eNB totransmit data, the UE receiving the downlink signal from the aggressoreNB may not obtain the control information of the ABS (p+1).

To solve this problem, a sub-frame indicator is added in the PDCCHcontrol signal for indicating whether the PDCCH control signal isutilized to describe the resource allocation of a current sub-frame orone or more sub-frame following the current sub-frame. For example, thesub-frame indicator may be a one bit indicator to indicate whether thePDCCH control signal carried in the current sub-frame is the controlsignal for the current sub-frame or a sub-frame following the currentsub-frame. The controller module (such as the controller module 230) ofthe UE receiving the downlink signal from the aggressor eNB may knowwhether the PDCCH control signal carried in the current sub-frame is thecontrol signal for the current sub-frame or a sub-frame following thecurrent sub-frame after decoding the sub-frame indicator.

Besides adding a sub-frame indicator in the PDCCH control signal, theaggressor eNB may further inform the UE about a start position of thedata region of the ABS (such as the sub-frame (p+1) shown in FIG. 15) ina different way. For a normal frame (such as the sub-frame p shown inFIG. 15), the eNB may carry information regarding a start position ofthe data region of the sub-frame p in the PCFICH control signal, andtransmit the PCFICH control signal in a control region of the sub-framep. Therefore, the UE may obtain information regarding the start positionof the data region of the sub-frame p from the PCFICH control signal.

However, for an ABS (such as the sub-frame (p+1) shown in FIG. 15),because the PCFICH control signal is not transmitted in the controlregion of an ABS, the eNB can not carry the information therein.Therefore, according to a first embodiment of the invention, the eNB mayset a start position of the data region of the ABS according to amaximum control region size defined by the communications system. Themaximum control region size may be, for example and not limited to, 3 or4 OFDM symbols, depending on the bandwidth of the OFDM carrier. In thismanner, the start position of the data region is fixed of each ABS andthus, the eNB does not have to inform the UE where the start positionis. FIG. 16 is a flow chart showing a method for cross sub-framescheduling for ABS according to a first embodiment of the invention. Aspreviously described, when the data region of a second sub-frame, whichis an ABS following a first sub-frame, is utilized by an eNB to transmitdata, the eNB may first carry a sub-frame indicator in a first controlsignal to be transmitted in a control region of the first sub-frame toindicate an UE that the second sub-frame following the first sub-frameis an almost blank sub-frame (Step S1602). Next, the eNB may set a startposition of the data region of the second sub-frame according to amaximum control region size defined by the communications system (StepS1604). Finally, the eNB may carry data in the data region from thestart position of the second sub-frame (Step S1606).

According to a second embodiment of the invention, the eNB may set astart position of the data region of an ABS in a conventional way (i.e.depending on the practical data size) and, instead of carrying theinformation in the control region, the eNB may further inform the UE ofthe information regarding the start position via radio resource control(RRC) signaling. FIG. 17 is a flow chart showing a method for crosssub-frame scheduling for ABS according to a second embodiment of theinvention. As previously described, when the data region of a secondsub-frame, which is an ABS following a first sub-frame, is utilized byan eNB to transmit data, the eNB may first carry a sub-frame indicatorin a first control signal to be transmitted in a control region of thefirst sub-frame to indicate an UE that the second sub-frame followingthe first sub-frame is an almost blank sub-frame (Step S1702). Next, theeNB may set a start position of the data region of the second sub-frameand inform the user equipment of information regarding the startposition via RRC signaling (Step S1704). Finally, the eNB may carry datain the data region from the start position of the second sub-frame (StepS1706)

For the UE receiving the downlink data comprising a plurality ofsub-frames from the eNB, the UE may obtain information regarding a startposition of the data region, the resource allocation and modulation andcoding scheme of the data signals of an ABS in a corresponding way. FIG.18 is a flow chart showing a method for cross sub-frame scheduling forABS according to a third embodiment of the invention. The UE may firstobtain a sub-frame indicator carried in a first control signaltransmitted in a control region of a first sub-frame received from aneNB (Step S1802) and determine whether a second sub-frame following thefirst sub-frame is an almost blank sub-frame (Step S1804). When thesub-frame indicator indicates that second sub-frame is not an ABS, theUE may obtain information regarding a start position of a data region ofthe second sub-frame from a second control signal transmitted in acontrol region of the second sub-frame (Step S1806). Otherwise, the UEmay obtain information regarding the start position of the data regionof the second sub-frame according to predetermined information nottransmitted in the control region of the second sub-frame (Step S1808).As previously described, the predetermined information may be fixed as amaximum control region size defined by the communications system and theeNB may not further inform the UE about this. In other embodiments, whenthe start position is not fixed and may be dynamically changed by theeNB, the eNB may inform the UE about where the start position is via RRCsignaling, so that the UE may obtain the predetermined informationtherefrom.

FIG. 19 is a flow chart showing a method for a communications system toassign an ABS pattern according to an embodiment of the invention. Inthe embodiment, one or more neighbor eNB(s)'s information is firstcollected (Step S1902). The information may comprise, but not limitedto, the neighbor eNB(s)'s signal power, received signal power of one ormore UE(s) served by the eNB(s), the interference measured by the UE(s)served by the eNB(s), or others. Next, at least one victim eNB whichserves one or more UE(s) interfered by the communications system isidentified based on the collected neighbor eNB(s)'s information (StepS1904). Finally, the ABS pattern is assigned to the victim eNB such thatan interference within a cell of the victim eNB is reduced (Step S1906).According to the embodiment, the ABS pattern may be assigned accordingto a predetermined configuration of the communications system or apredetermined configuration of the victim eNB. The predeterminedconfiguration may be the previously described FDD configuration or TDDUL/DL configurations 0-6. For example, the ABS pattern may be assignedaccording to the predetermined configuration of the aggressor eNB, orthe victim eNB. In addition, the ABS pattern may be assigned with aperiod of 8 sub-frames (for example, for the FDD configuration), 10sub-frames (for example, for the TDD UL/DL configurations 1-5), 60sub-frames (for example, for the TDD UL/DL configuration 6) or 70sub-frames (for example, for the TDD UL/DL configuration 0). Note thatthe neighbor eNB(s)'s information may further be updated so as toperiodically or a periodically adjust the assigned ABS pattern accordingto the updated information. Therefore, by assigning the ABS, theinterference within a cell of the victim eNB can be reduced.

Use of ordinal terms such as “first”, “second”, “third”, etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. Those who are skilled in this technology can still makevarious alterations and modifications without departing from the scopeand spirit of this invention. Therefore, the scope of the presentinvention shall be defined and protected by the following claims andtheir equivalents.

What is claimed is:
 1. A method for coordinating transmissions betweendifferent communications apparatuses in a communications system,comprising: obtaining information regarding a Hybrid Automatic RepeatRequest (HARQ) round trip time (RTT) in an HARQ process defined by thecommunications system; and arranging one or more almost blanksub-frame(s) in one or more frame(s) according to the HARQ RTT.
 2. Themethod as claimed in claim 1, wherein at least one almost blanksub-frame is arranged in a sub-frame utilized by a communicationsapparatus to transmit an uplink grant message for granting an userequipment to transmit uplink data to the communications apparatus. 3.The method as claimed in claim 2, wherein at least one almost blanksub-frame is arranged in a sub-frame utilized by a communicationsapparatus to transmit an acknowledgment (ACK) or a negativeacknowledgment (NACK) message for informing the user equipment aboutwhether the uplink data transmitted by the user equipment in response tothe received uplink grant message have been received by thecommunications apparatus.
 4. The method as claimed in claim 1, wherein asub-frame index of the almost blank sub-frame(s) is arranged to be fixedin different frames.
 5. The method as claimed in claim 1, wherein whenthe HARQ RTT is defined by (k1+k2) sub-frames, the almost blanksub-frame(s) is/are arranged in the [n+m*(k1+k2)]-th sub-frame(s) foreach n-th sub-frame is assigned as an almost blank sub-frame, wherein nand m are non-negative integers, k1 and k2 are positive integers, k1represents a sub-frame offset between an uplink grant messagetransmission and uplink data transmission, and k2 represents a sub-frameoffset between the uplink data transmission and an ACK or a NACK messagetransmission.
 6. The method as claimed in claim 1, wherein the almostblank sub-frame(s) is/are arranged according to a transmission period ofan uplink grant message and an acknowledgment (ACK)/negativeacknowledgment (NACK) message, wherein the uplink grant message istransmitted for granting an user equipment to uplink data and theACK/NACK message is transmitted for informing the user equipment aboutwhether the uplink data transmitted in response to the received uplinkgrant message have been received.
 7. The method as claimed in claim 1,wherein the almost blank sub-frames are arranged in a series ofcontiguous frames.